316 
POPULAR SCIENCE REVIEW. 
Light is the winged messenger to whom w^e bend for infor- 
mation. Every one of the objects to which we have directed 
attention in the heavens is rendered sensible to us by its light 
alone. Light may be dimmed in its passage through the 
immensity of space; its undulations maybe weakened, bke the 
pulsations of a bell communicated to the air. They may, they 
do, eventually sink into rest, which, in the case of sound, is 
silence; in the case of light, it is darkness, or invisibihty. 
Yet, howsoever faint may be the waves which reach the eye, 
they still are light rays — possessing yet all the peculiarities 
which have been given to them by the physical condition of 
the bodies from which they have originated. It has been 
already explained* that light results from some change in the 
form of matter — that this change is ordinarily combustion ; but 
that there are other changes — modes of motion — by which 
luminous phenomena may be produced. We know, however, of 
no means by which light can be developed without an alteration 
in the condition of the material particles which are concerned 
in the production of luminous energy. As the light of the 
Sun is due to the alterations which are constantly going on 
in the matter of which the Sun is formed, it is more than 
probable that the light of the fixed stars is produced by 
similar disturbances. We have no reason for supposing 
that the planetary and stellar globes which float so beautifully 
in space, are in any remarkable degree differently constituted 
from our own Earth. We have determined that a certain 
number of bodies — sohd, fluid, or gaseous — to which we give 
the name of elements, combine to form all the varieties 
of terrestrial matter. There may be bodies, regarded by 
us as simple, which are compound, and with the advance of 
knowledge we may discover ' other elements than those 
with which we are now acquainted. This is not important 
to our inquiry, which is to learn if other worlds contain. 
any of the substances which constitute the matter of this 
world. It has been shown, in the papers already referred 
to, that when any of those elements, or compounds of those 
elements, are diffused as vapour in flame, they impart peculiar 
characteristics to the flame. It has also been sufficiently ex- 
plained that by examining the flame with the spectroscope 
apparatus, we can determine with minute accuracy the kind 
of substance which is giving character to it.f Turning 
the same apparatus to the Sun, we find evidence which as- 
* Popular Science Review, Vol. IV. — “The Source of Heat in the 
Sun,” and Vol. I., pp. 205 and 299. 
t See “ On the Spectra of some of the Chemical Elements.” By William 
Huggins, Esq., E.R.A.S. “ Philosopliical Transactions,” vol. 154, part iL, 
page 139. 
